In particular, yet not restrictive manner, the invention concerns a mechanical locking system for rectangular floor panels with long and short edges. It should be emphasized that long and short edges are only used to simplify the description. The panels could also be square. However, the invention is as well applicable to building panels in general. More particularly the invention relates to the type of mechanically locking systems which allow that all four edges of a panel could be locked to other panels by a single angling action preferably comprising a flexible or partly flexible tongue and/or displaceable tongue and/or a flexible locking strip in order to facilitate the installation of building panels.
A floor panel of this type is presented in WO2006/043893, which discloses a floor panel with a locking system comprising a locking element cooperating with a locking groove, for horizontal locking, and a flexible tongue cooperating with a tongue groove, for locking in a vertical direction. The flexible tongue bends in the horizontal plane during connection of the floor panels and makes it possible to install the panels by vertical folding or solely by vertical movement. By “vertical folding” is meant a connection of three panels where a first and second panel are in a connected state and where a single angling action of a new panel referred to as the “folding panel”, connects two perpendicular edges of the new panel, at the same time, to the first and second panel. Such a connection takes place for example when a long edge of the first panel in a first row is already connected to a long edge of a second panel in a second row. The new folding panel is then connected by angling to the long edge of the first panel in the first row. This specific type of angling action, which also connects the short edge of the new folding panel and second panel, is referred to as “vertical folding”. The short edges are gradually folded together and locked from one edge part to the other as scissors when the panel is angled down to the subfloor. It is also possible to connect two panels by lowering a whole panel solely by vertical movement against another panel. This specific type of locking is referred to as “vertical locking” A first row in a flooring system, which is designed to be locked with vertical folding, is often connected with a vertical locking where one short edge is pressed down vertically towards an another short edge. The other rows are connected with vertical folding. It is also possible to install a complete floor by connecting a row with vertical locking. The whole row is than connected to a previous installed row by angling.
Similar floor panels are further described in WO2003/016654, which discloses locking system comprising a tongue with a flexible tab. The tongue is extending and bending essentially in a vertical direction and the tip of the tab cooperates with a tongue groove for vertical locking.
Vertical locking and vertical folding of this type creates a separation pressure at the short edges when the flexible tongue or flexible parts of the tongue are displaced horizontally during the angling of the long edges. The inventor has analysed several types of floor panels and discovered that there is a considerable risk that the short edges could be pushed away from each other during installation and that a gap could occur between the edge portions of the short edges. Such a gap could prevent further installation and the floor panels will not be possible to connect. It could also cause serious damage to the locking system at the short edges. Pushing the floorboards sideways towards the short edges during installation could prevent the gap. Such an installation method is however complicated and difficult to use since three actions have to be combined and used simultaneously in connection with angling down of the long edges as described below.
a) The edges of a new floor panel has to be brought in contact with a first floor panel laying on the floor and the long edge of the new panel has to be pressed forward in angled position towards the first panel
b) The new panel has to be displaced sideways, in the pressed and angled up position, and pressed sideways against a short edge of a second panel laying on the floor in order to counteract the counter pressure of the tongue
c) The new panel must finally be angled down to the floor and the forward and sideways pressure must be maintained during the angling action.
The inventor has discovered that separation and installation problems often occur when the panels have a small thickness and small compact locking systems on the long edges or when the panel core comprise a material with smooth surfaces such as high density fibreboard (HDF). Such problems could also occur when the panels are short or in connection with the installation of the first or last panel in each row since such installation is generally made with panels which are cut to a smaller length in order to adapt the floor to the wall position. Separation problems are of course extremely difficult to handle in any type of panels using locking systems with a strong flexible tongue that creates a substantial horizontal separation pressure during the vertical folding. Such strong tongues are very important in many applications where a high quality vertical connection is required and panels with such flexible tongues are very difficult to install with the known installation methods.
The invention aims to solve separation problems in flooring which is intended to be installed with vertical folding or vertical locking.